1. Field of the Invention
The present invention relates generally to systems for providing fusing energy to print media. More particularly, the present invention relates to a method and apparatus for providing variable fusing energy to print media so as to selectively vary the gloss of the final product without varying the process speed.
2. Related Art
In color printing (i.e. color laser printing and photocopying), fusing plays a large part in determining the level of gloss of the printed output. Transmitting thermal energy to the print media to fuse the toner is an important part of the process. Typical fusing temperatures range from 160° to 190° C., while typical paper media burns at approximately 230° C. Additionally, many of the typical materials used in fusers (e.g. silicone rubber) do not perform well at temperatures above 200° C.
These factors combine to determine the range of acceptable temperatures available for fusing. Generally, a greater amount of thermal energy will produce a higher gloss. However, it is undesirable to scorch or deform the media. Media deformation typically increases with increased fusing temperatures. This is due, many times, to the fact that the peak temperature of fusing can vaporize water contained in the paper. This can produce wave, curl, cockling, and stretch or shrinkage. These types of media deformation are not desirable.
Accordingly, it is desirable to be able to vary the amount of thermal energy which is transmitted to the media to vary the gloss. Conventionally, the most common method used to provide variable fusing energy to printed media is to vary the process speed. By slowing the page down, it has more time to acquire the thermal energy provided by the fuser. However, with this method, the printer throughput, i.e. the rate at which pages may be processed, is decreased as the process speed is decreased. Another method conventionally used to provide variable fusing energy is to change the temperature of the fusing element, typically a heated roller. This latter method can provide increased thermal energy to the print media as well. However, the electrophotographic process does not provide for a large range in which to adjust the temperature, for the reasons mentioned above, and thereby, the amount of thermal energy, fusing (and gloss imparted). The thermal mass of the element typically makes it difficult to change the temperature in a short time period. Moreover, this latter method can tend to deform the media due to excessive temperature levels.